This invention relates to a new isolate of a cold tolerant Trichoderma species (hereafter "the Trichoderma isolate"). This invention also relates to mutants of the Trichoderma isolate that are resistant to commercially available pesticides, such as Benomyl and Ridomil.
This invention further relates to a method for the control of the transmission and spread of plant disease by applying an agriculturally effective amount of cold tolerant Trichoderma or a pesticide resistant cold tolerant Trichoderma mutant to a plant or plant tissue to be protected from a fungal pathogen. This invention also relates to a method for the treatment of plant disease by applying an agriculturally effective amount of the Trichoderma isolate or a pesticide resistant mutant of the Trichoderma isolate to a plant or plant tissue to be treated.
This invention still further relates to a method of promoting the growth and development of a plant by applying an agriculturally effective amount of the Trichoderma isolate or Benomyl resistant mutants of the Trichoderma isolate to a plant or plant tissue.
This invention also relates to three molecules associated with the Trichoderma isolate, that are useful for the control and treatment of plant disease.
Plant pathogens such as soil-borne pathogenic fungi are well recognized agricultural problems causing extensive damage, including damping off, white rot, wilt, southern rot, snow mold, root rot, black scurf, and grey mold to various commercially important crops. For example, these fungi have been found to cause extensive damage to wheat, barley, oats, grasses, cotton, potatoes, tomatos, peas, vegetables, flowers, grapes, strawberries, pistachio, almond, apples, cherries, peaches, nectarines, pears, persimmons, plums, prunes, olives, walnuts, trees, and shrubs and thus pose serious problems to the agriculture, horticulture, and forestry industries. In the past the major approach in controlling these pathogens has been through the use of chemical pesticides. However, due to important economic and ecologic considerations, their use has been disfavored and alternative approaches are sought.
Recently, the biological control ("biocontrol") of plant pathogens has been achieved. For example, the control of many pathogenic fungi through the use of antagonistic microorganisms has been demonstrated for several species of Trichoderma. While it has been found that different species or strains within a species of Trichoderma may be differentially antagonistic to different pathogenic fungi, Trichoderma viride and Trichoderma harzianum have been shown to be generally effective as biocontrol agents. Some of the possible advantages associated with the biocontrol of pathogenic fungi through the application of Trichoderma as compared to the use of chemical pesticides include an improvement in food safety, a reduction of pollution in the environment, and a decreased incidence of occupational disease to workers in the industry.
The usefulness of T. viride and T. harzianum is greatly limited in certain situations due to their intolerance to low temperatures. Because many plant pathogens, such as Pythium spp., are most destructive in cool soils, the inability of these Trichoderma species to grow and function in these soils leaves the plants without protection at the time of greatest need. It would be desirable, therefore, to obtain a microorganism that has the characteristics of T. viride and T. harzianum as biocontrol agents and yet be sufficiently capable to withstand cold temperatures to function as biocontrol agents in cool soils.
Such a cold-tolerant biocontrol agent would be especially useful in high-latitude regions. By way of example, snow mold, a disease caused by low temperature pathogenic fungi, is the major cause of crop failures of winter cereals, such as wheat, rye, triticale, and barley, making it very difficult to establish a winter cereal industry in Alaska as well as other high-latitude regions.
The organisms Sclerotinia borealis, Fusarium nivale, sclerotial low temperature basidiomycete (sLTB), Coprinus psychromobidus (i.e., low temperature basidiomycete-LTB) and Typhula spp. are implicated as the most prevalent causative agents of this fungal disease. These fungi infect host plants in late fall or winter when the soil is not yet frozen. During the long winters in the dark, humid conditions found under a thick snow layer, the fungi proliferate and spread in the host tissues. This parasitic relationship between the host and the parasitic fungi results in the rapid depletion of nutrient reserves, destruction of plant cells by extracellular enzymes, and the eventual death of the host plants. Consequently, the effective control of snow mold disease through the application of a cold tolerant Trichoderma may very well permit farmers in Alaska or other areas where the growing season is short to cultivate new crops, such as winter cereals.
There is a need, therefore, in the art for a biocontrol agent that is effective against snow mold as well as other plant diseases caused by pathogenic fungi at low temperature.
There also exists a need for a biocontrol agent that would be generally effective against fungal plant pathogens that exist under more moderate conditions as well as at low temperatures. The number and variety of fungi that are plant pathogens under moderate conditions is extensive. Among the Phycomycetes examples of important plant pathogens are Pythium which causes damping off, Peronospora tabacina which causes blue mold of tobacco, and Phytophthora infestans which causes late blight of potato. Among the Basidiomycetes examples of plant pathogens include Armillaria sp. which causes root rot and Typhula spp. which causes snow mold. Among the Ascomycetes, examples of plant pathogens include Sclerotinia sclerotiorum and S. borealis which cause white rot and snow mold, respectively. Among the Deuteromycetes examples of important plant pathogens include Botrytis sp., Verticillium sp., Fusarium sp., Sclerotium sp., and Rhizoctonia solani which are responsible for plant diseases such as wilt disease on fruit trees, vegetables, and potatoes, white rot diseases of beans, carrots, and onions, gray mold of fruits and seedlings, root rot, black scurf and damping off.
Consequently, there exists a need in the art for a biocontrol agent that is effective against a wide range of pathogenic fungi existing at moderate as well as low temperatures.